Folia Geobot. Phytotaxon., 13: 400, 1978. Basionym: Biatora diaphana Körb. ex Nyl. - Act. Soc. Linn. Bordeaux, 21: 352, 1856.
Synonyms: Bacidia bayeri (E. Senft) Servít; Biatorina diaphana (Nyl.) Körb.; Catillaria bayeri E. Senft; Catillaria diaphana (Nyl.) Lettau
Distribution: C - Tosc.
Description: Thallus crustose, thinly episubstratic, continuous to rimose, dark brown to brown-black, subgelatinous when wet. Apothecia lecideine, subsessile, 0.2-0.4 mm across, with a concave to flat, dark brown to black disc (turning violet-grey and slightly translucent when wet), and a thin, more or less raised proper margin. Proper exciple well-developed, dark; hymenium colourless, 70-85 μm high, I+ reddish brown; paraphyses simple, up to 1.5 µm thick, slightly swollen at apex, immersed in a gelatinous matrix; hypothecium colourless. Asci 8-spored, cylindrical-clavate, thin-walled except for a slightly thickened apical tholus reacting K/I-, and a small ocular chamber. Ascospores 1(-3)-septate, hyaline, ellipsoid to fusiform, 8-12(-15) x 5-6 μm. Pycnidia black, immersed in the thallus. Conidia bacilliform, 7-12 μm long. Photobiont chlorococcoid, Leptosira-like. Spot tests: thallus K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: on periodically submerged micaceous rocks near brooks, with optimum in the montane belt; the species resembles G. fritzei but has one-septate ascospores. The Italian record needs confirmation (see Nimis 1993: 310).